Apparatus for pelleting powdered materials



Aug. 21, 1962 C) us m 3,049,750

APPARATUS FOR PELLETING POWDERED MATERIALS Filed April 25, 1960 LOOSE VIBRATOR INVENTOR. O. K. AUSTIN BYM/fiM chamber.

United States Patent 3,049,750 AlPARA'IUS FOR PELLETlNG POWDEREB MATERIALS ()liver K. Austin, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Apr. 25, 1960, Ser. No. 24,515 8 Claims. (Cl. 181) This invention relates to an improved apparatus for the wet pelleting of powdered materials.

Dry ilocculent carbon black and other powdered materials such as catalyst powders are conventionally pelleted in admixture with aqueous liquid in pug mills.

US. Patent 2,550,802 discloses such pug mills. The water and powdered materials to be pelleted are introduced into the upstream end of the mill where the liquid and solids are mixed and moved thru the mill toward the delivery end thereof. As the mixture is moved thru the mill by the pins on the axial shaft of the mills, pellets are formed and these egress from the foot or delivery end of the mill. Each mill requires separate feed and control means on both the water and powdered material feed lines. This invention is concerned with an improved pelleting mill which costs less to build and to operate than conventional pug mills of the same capacity.

Accordingly, it is an object of the invention to provide an improved apparatus for the wet pelleting of powdered materials. Another object is to provide an arrangement of pug mills for wet pelleting of carbon black and similar powdered materials which is less expensive to build and operate than conventional pug mills of similar capacity. A further object is to provide pelleting apparatus which requires less man-hours to operate. Other objects of the invention will become apparent upon consideration of the accompanying disclosure.

In accordance with the invention, two pug mills are arranged with their axes parallel in the same horizontal plane and with their shells contiguous. The upstream ends of the mills are open and are enclosed by a mixing The axial shafts of the two mills continue thru the mixing chamber and are provided with helical or screw feeders on the upstream end of the shafts adjacent the remote end of the mixing chamber. A single feed conduit for powdered material enters the mixing chamber adjacent the upstream end and is positioned to deliver powdered solids onto and between both screws to effect mixing of the solids and water, the latter being delivered to the mixing chamber adjacent the feed conduit by one or more sprays. The pins on the axial shafts of the two mills begin adjacent the downstream end of the screw on each shaft which extends at least as far downstream as the downstream side of the solids feed conduit. These pins extend at spaced intervals in a helical pattern along the shaft to the delivery end of each mill.

A single water line with a single set of controls feeds the water sprays. The powdered solids are fed into the feed-in conduit by a single conveyor, preferably, a vibrascrew conveyor, requiring only one motor and one set of controls. The shafts of the mills are arranged so as to operate from a single motor with a single set of controls.

A more complete understanding of the invention may be had by reference to the accompanying schematic drawing which is an isometric view with cutaway section showing a preferred arrangement of the apparatus of the invention.

Referring to the drawing, a pair of pug mills 1i) and 12 are positioned with their axes in the same horizontal plane and with their shells contiguous. The upstream ends of the mills are open and are enclosed by mixing chamber 14. This mixing chamber is formed by extending the opposite upright sides of mills ll) and 12, each comprising a half cylinder tangent at its midpoint to a vertical plane, upstream a sufficient distance to provide adequate mixing space, and providing top and bottom walls 15 and 18, respectively, which are tangent to the extended semi-cylindrical walls forming the lateral sides of the chamber, and the upstream end of the mixing chamber, formed by a vertical Wall at right angles to the mill axes. A pair of downstream end walls 22 close the mixing chamber between the mills. Feed conduit 23 is positioned at the upstream end of chamber 14 with its axis midway between the shafts of the mills and tangent to the inner side of wall 20.

Each mill is provided with an axial shaft 24 and with pins 25 forming a helical pattern along the shaft. The upstream ends of the shafts 24 are provided with screws 255 which extend downstream at least as far as directly below the downstream side of the feed conduit 23. Three water sprays Stl are grouped in close proximity to the inlet end of conduit 23 in order to provide good mixing of the solid material and water.

Water sprays 3% connect with a common water line 32 which is provided with a motor valve 34 and with a flow controller 36. This flow controller can be set at any desired rate of liquid flow and can be re-set from time to time in accordance with changing conditions within the mills.

Shafts 2- of the two mills extend thru wall 2% and are provided with pins 26 and with gears 38 and 44) which mesh with each other and cause clockwise and counterclockwise rotation of the respective mill shafts when either gear is driven. The gears are driven by driving gear 42 which is on the shaft of motor 44.

Feed conduit 23 leading into the top of chamber 14 connects with the underside of vibra-screw feeder 46 which contains screw 48 and is vibrated by a vibrator 50. Motor 52 operates screw 48. A downcomer 54 from a hopper not shown delivers powdered solids to conveyor 46.

Outlet conduits 56 and 58 connect with the mill outlets and converge to a delivery spout 69 which leads to a pellet polisher (not shown).

The mills are preferably about 24 inches in internal diameter but may range from 6 to inches ID. The shafts of the mills are preferably of a diameter in the range of about 4 and the pins are preferably /2" in diameter and one inch center to center longitudinally of the shaft and offset to provide a helical pattern. The pins in a 24 ID. mill are 22 long and pass thru the center of the shaft at a slight angle to extend to within about 1" of the shell at either end. In conventional mills, each pin is a separate pin extending from the shaft to the proximity of the shell at right angles, to the shaft. The pins can be utilized until they wear down to a spacing of as much as 4 clearance with the mill shell before replacing them is required. Mills 14 and 12 are preferably about 8 feet in length but may deviate a foot or two either way from this preferred length. Chamber 14 should be long enough to provide complete mixing of the solids and aqueous liquids before the mixtures are moved into the pug mills. A length of 2 /2 to 3 feet is preferred but this length may Vary from about 2 to 4 feet. Actually, pellets are formed in the section of the mixer which contains pins 25 so that the material entering the separate cylinders is largely pellets. The pelleting and compacting of pellets continues in these cylinders.

In a mill constructed in accordance with the preferred dimensions of the mills and mixing chamber recited above, a 12 feed conduit 23 is positioned tangent to the upstream wall of chamber 14 directly above the center line between the screws. With this arrangement, screws (2 28 are at least 12 inches in length and preferably 15 inches long. The shafts in the mills are preferably operated at about 300 rpm. but may be operated in the range of 200 to 400 rpm. to produce satisfactory pellets.

The proportion of water when pelleting carbon black must be controlled within the range of 4-2 to 58 percent water based on the Weight of the mixture of carbon black and water. If more water is utilized than this specified range, the mixture forms a mud in the equipment which defies pelleting and requires a shut-down. If less than the specified amount of water is utilized, the pellets produced are excessively dusty.

Using an apparatus of the preferred dimensions, it is normal operation to pellet 90,000 pounds of black per day and this equipment may be utilized to pellet from 45,000 to 120,000 pounds carbon black per 24 hour day. A twenty horsepower motor operating the mixer shafts at 300 rpm. is sufficient to operate the unit described.

The liquid utilized in the process may contain additives such as wetting agents, molasses, etc., in small concentrations, such as 0.25 to weight percent. In pelleting carbon black, molasses is mixed with water to provide a solution containing about 0.1 to 4 percent molasses. The range of 42 to 58 percent aqueous solution specified as the range of water concentration in the mixture of carbon black and water covers the extreme limits permissible if effective pelleting is to be obtained. The maximum and minimum amount of water will vary slightly with the type of black, its photelometer, the water temperature, and the type and concentration of additives utilized. Usually the use of 50 percent water and 50 percent carbon black in the mixture produces excellent pelleting.

The apparatus described has a capacity of about 5,000 pounds of black per hour. This device has numerous advantages over two separate pug mills each operating at 2,500 pounds per hour of carbon black. One set of feed controls, one drive for the mixer, and one drive for the polisher are required with the device of the invention as compared with one each for two conventional pug mills producing the same amount of pellets. In addition the device of the invention requires less expensive inlet and outlet connections and also less operation and maintenance labor. To illustrate, proper operation of the mills requires the operator to look into the mills every minutes to observe the character of the pellets being produced and to make minor adjustments of the amount of water and/ or loose black feed to the apparatus at less frequent periods, such as once every hour. Obviously, it takes less time to change one set of controls than it does to change two sets of controls.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

1 claim:

1. Wet pelleting apparatus comprising in combination, a pair of cylindrical pug mills arranged with their axes parallel and in a horizontal plane and their shells contiguous but closed to each other therebetween, each said mill being provided with an axial shaft with radial pins thereon; an enclosed common mixing chamber attached to and enclosing the upstream ends of said mills, said ends being open to said chamber and the axial shafts of said mills extending thru said chamber; a feed conduit in the top of said chamber adjacent the end remote from said mills; a feed screw on the upstream end of each said shaft extending at least to a point just below the downstream side of said feed conduit, said radial pins on said shaft commencing adjacent said screw and being spirally arranged; water spray means in an upper section of said chamber; and means for withdrawing pellets from the downstream ends of said mills.

2. The apparatus of claim 1 including a feeder for powdered material connected with said feed conduit; and a variable speed motor on said feeder.

3. The apparatus of claim 2 wherein said feeder is a vibra-screw feeder.

4. The apparatus of claim 1 wherein said water spray means comprises a plurality of sprays within said chamber connected to a common water supply line and includin g flow control means in said line.

5. The apparatus of claim 1 wherein said means for withdrawing pellets comprises a pair of conduits converging from outlets in the downstream end of said mills to a common delivery conduit.

6. The apparatus of claim 1 wherein said chamber comprises an upright end Wall on its upstream end, side walls in the form of half-cylinders forming an extension of the opposite remote side walls of said cylindrical shells, and

- top and bottom walls in horizontal planes tangent to said half-cylinders.

7. The apparatus of claim 1 including a gear on the end of each shaft outside the upstream end of said chamber, each gear meshing with the other so as to drive one shaft clockwise and the other counterclockwise.

8. Wet pelleting apparatus for pelleting flocculent carbon black comprising in combination, a pair of cylindrical pug mills arranged with their axes parallel and in a horizontal plane and their shells contiguous but closed to each other therebetween, each mill being provided with an axial shaft with radial pins thereon forming a helical pattern; an enclosed common mixing chamber attached to and enclosing the upstream ends of said mills, said ends being open to said chamber and the axial shafts of said mills extending thru said chamber and the end wall thereof opposite said mills; a feed screw on the upstream end of each of said shafts in lieu of said pins, said pins commencing adjacent said screw extending at least to a point just below the downstream side of the herinafter named feed conduit and said screws; a feed conduit in the top of said chamber directed toward the area between said screws; a carbon black feeder connected with said feed conduit; a plurality of water sprays in said chamber positioned to spray water in the area of said screws and connected to a common water line; flow control means in said water line; common means for rotating said shafts; and a pair of effiuent pellet conduits each connecting the outlet of one of said mills with a common delivery conduit.

References (Iited in the file of this patent UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,049J50 August 21, 1962 Oliver K. Austin It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, lines 42 to 45, for "pins commencing adjacent said screw extending at least to a point just below the downstream side of the h 'i aft r named feed conduit and" read screw extending at least to a point just below the downstream side of the hereinafter named feed conduit and said pins commencing adjacent Signed and sealed this 6th day of August 1963.

(SEAL) Attest:

DAVID L. LADD ERNEST W. SWIDER Commissioner of Patents Attesting Officer 

